A novel bonding mode of a deprotonated syn-anti 2,2'-dipyridylamine ligand to dimethyl aluminium and dimethyl gallium. Synthesis, characterization and X-ray crystal structure of Me(2)Ga(DPA) (DPA=2,2'-dipyridylamine)

The reaction of 2,2'-dipyridylamine with R(3)M (R = CH3, M = Ga, Al) gave the Lewis acid-base adducts Me(2)Ga(dpa) and Me(2)Al(dpa) (where dpa is 2,2'dipyridylamide). X-ray analysis showed an unusual structure of dpa(-) in the formation of a new anti-anti complex Me(2)Ga(dpa) with extremely short bond distances Ga-N(1) [1.976(3) Angstrom] and Ga-N(2) [1.978(3) Angstrom]. The gallium atom is in a tetrahedral environment, coordinated to the deprotonated chelating ligand and two methyl groups. The bond distances N(3)-C(5) [1.345(4) Angstrom] and N(3)-C(6) [1.347(4) Angstrom] are almost identical. The bond angle N(1)-Ga-N(2) [92.0(1)degrees] is 17 degrees smaller than, and C(12)-Ga-N(1) [109.5(2)degrees] is almost equal to, normal tetrahedral angles. These adducts are much less air- and moisture-sensitive than the metal trialkyl. The compounds were characterized by elemental analysis, NMR and mass spectroscopy. The conformation of the dipyridylamide ligand in the bidentate chelate complex is significantly different from that observed for other dipyridylamine complexes. Copyright (C) 1996 Elsevier Science Ltd